A Longer Life May Not Be In Your Genes

January 27, 2021

Longevity tends to run in families, a phenomenon often attributed to people’s genes. But now, a large new study of data from the genealogy website Ancestry suggests that genetics may play a smaller role in longevity than previously thought.

The reason? Previous studies have failed to take into account a quirk of human relationships: the tendency for people to choose romantic partners with characteristics similar to their own. The findings mean that previous studies may have greatly overestimated the heritability of lifespan, the researchers said.

The study is published today (Nov. 6) in the journal Genetics. It was funded by Calico Life Sciences, a research and development company owned by Alphabet Inc. (Google’s parent company) with funding from Calico Life Sciences, a research and development company whose mission is to understand the biology of aging.

“Anabolic Mating”
In a given population, people will vary a lot; they will have different heights, eye colors, and, yes, life spans.

Heritability is a measure of how much variability in a trait, such as life expectancy, is explained by the variability in people’s genes, in contrast to environmental factors such as a healthy diet or exercise. Previous studies have estimated heritability for life expectancy as high as 30 percent.

In the new study, researchers analyzed information on more than 400 million people using Ancestry’s publicly available family tree. Because researchers needed to know the lifespans of these people, the study only looked at those who were born in the 19th or early 20th century and had died. (Before sharing this data, Ancestry removed all identifiable information from the genealogy).

Preliminary analyses show that when comparing the lifespans of siblings and first cousins, the heritability of lifespans appears to be around 20 to 30 percent – similar to the findings of previous studies.

But spouses’ lifespans also tended to be similar. The study says this may be due to the fact that spouses share similar environments. Because they live in the same household, they may share many non-genetic factors, from diet to sleep habits, that could affect lifespan.

But then the researchers noticed something odd: they found that the lifespans of even sibling in-laws and first cousins are correlated, even though they don’t generally live in the same family and aren’t blood relatives.

But if they didn’t have close family histories or similar environments, why were the lifespans of distant relatives and non-blood relatives correlated as well? The large dataset has allowed researchers to study the effects of so-called assortative mating, the phenomenon where people tend to choose mates who are similar to them. Graham Ruby, lead author of the study and lead researcher at Calico Life Sciences, said in a statement: “If it’s assortative mating at work, it would imply that factors important to lifespan tend to be similar between mates.

Indeed, the researchers found that this was the case, with the heritability of life expectancy dropping to 7 percent when they took into account assortative mating.

However, this study doesn’t mean that people will choose a mate based on their lifespan, because that’s not possible, says Ruby.” Generally, people will marry before one of them dies,” Ruby joked.

But other factors may also be at play, including genetic and non-genetic variables. For example, researchers say that if wealth is tied to life expectancy, and rich people tend to marry other rich people, that could make life expectancy seem more heritable than it really is. Or, if height – a trait that is partly influenced by genetics – is associated with longevity, and tall people tend to marry other tall people, that could also confound analyses of the heritability of longevity.

However, the results of the study do not imply that there are no genes for longevity. The study focused on heritability of longevity at the population level and did not specifically look at people’s genomes. Previous studies have found a link between certain genes and longevity.